342 Archdeacon Pratt on the Curvature of the Indian Arc. 



would be counteracted by a counter or negative attraction arising 

 from a deficiency of matter below*. It is assumed that the in- 

 terior of the earth is fluid, and that the crust is sufficiently thin 

 to allow the principles of hydrostatics to regulate the external 

 form of the surface, or that this was the state of things when 

 the surface took its present form. It is further assumed that 

 the soUd crust of the earth is light compared with the fluid mass 

 on which it floats. 



The case is then taken (fig. 1) of a table-land 2 miles high. 



Internal fluid. 



100 miles wide, and of indefinite length, — suggested, no doubt, 

 by the plateau from which the Indus and Brahmapootra flow, more 

 than 10,000 feet above the sea-level, and forming the most 

 important part of the attracting mass in my paper. The mean 

 crust is taken to be 10 miles thick, and therefore 12 at the table- 

 land. It is then conceived that the crust is broken through in the 

 dotted lines ab, cd, ef, where lies the greatest tendency to crack, 

 and the force of cohesion necessary to prevent the two portions 

 from sinking into the fluid below is estimated. The force is 

 found to be equal to a weight of 20 miles' length of the rock ; 

 and the conclusion is justly drawn, that as no such power of 

 cohesion can exist in the crust, the state of things represented 

 in fig. 1 cannot be that of nature. 



8. The hypothesis, as represented in fig. 2, is then suggested, 



Fig. 2. 



* See a paper in the Transactions of the Royal Society for 1855, " On 

 the Computation of the EfFect of the Attraction of Mountain Masses," &c., 

 by G. B. Airy, Esq., Astronomer Royal. 



